FlightAware Discussions

FA Antenna, Near Field effect

Just a quick note for those working to optimize your setup. I have observed a fairly noticeable difference between this antenna in a somewhat “clear space” versus when there are objects nearby. It is not an antenna flaw, it is simply physics. Any higher gain antenna should also exhibit the same characteristics. Nearby things affect how they operate…the higher the gain the more the affect.

If this antenna is not working well for you, you may want to make note of anything else in close proximity, I am not sure what the “boundary” distance might be, but assume that more free space is better…and now I’ll stay quiet as I know there are more folks here that are far more knowledgeable than I.

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That is nothing new. Many people have identified that obstacles can cause trouble

For an antenna 1m long, the reactive nearfiield, i.e, where the antenna is dramatically detuned and the radiation pattern is influenced, is closer than 1.2m, objects between 1.2m and 7,3m away, will still influence the antenna, but not as dramatically, mainly just change the radiation pattern a bit. Only objects that are further than 7m away wont influence the antenna. Even simple things, like a sleeve you put over your antenna, will influence it. It doesn’t help spending days to calculating,building, tuning and testing the perfect antenna, and when you are satisfied, you destroy it by putting a sleeve over it. If your antenna has to be protected by a sleeve, its effect has to be taken into consideration when you do the calculations.

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